OpenRouter Integration

Instrument OpenRouter model calls in Go with LangWatch to compare models, track quality, and run AI agent evaluations.

OpenRouter provides a unified API to access LLMs from many providers. LangWatch traces calls made through OpenRouter using its OpenAI-compatible endpoint.

Setup

You will need an OpenRouter API key from your OpenRouter settings.

Set your OpenRouter API key as an environment variable:

export OPENROUTER_API_KEY="your-openrouter-api-key"

Usage

Set LANGWATCH_API_KEY and OPENROUTER_API_KEY environment variables before running.

The key difference with OpenRouter is the model name, which is prefixed with the provider (e.g., anthropic/claude-sonnet-4-20250514).

package main

import (
	"context"
	"log"
	"os"

	langwatch "github.com/langwatch/langwatch/sdks/go"
	otelopenai "github.com/langwatch/langwatch/sdks/go/instrumentation/openai"
	"github.com/openai/openai-go"
	oaioption "github.com/openai/openai-go/option"
	"go.opentelemetry.io/otel"
	sdktrace "go.opentelemetry.io/otel/sdk/trace"
)

func main() {
	ctx := context.Background()

	// Set up LangWatch exporter
	exporter, err := langwatch.NewDefaultExporter(ctx)
	if err != nil {
		log.Fatalf("failed to create exporter: %v", err)
	}
	tp := sdktrace.NewTracerProvider(sdktrace.WithBatcher(exporter))
	otel.SetTracerProvider(tp)
	defer tp.Shutdown(ctx) // Critical: ensures traces are flushed

	// Create OpenRouter client via OpenAI-compatible API
	client := openai.NewClient(
		oaioption.WithBaseURL("https://openrouter.ai/api/v1"),
		oaioption.WithAPIKey(os.Getenv("OPENROUTER_API_KEY")),
		oaioption.WithMiddleware(otelopenai.Middleware("my-app",
			otelopenai.WithCaptureInput(),
			otelopenai.WithCaptureOutput(),
			otelopenai.WithGenAISystem("openrouter"),
		)),
	)

	response, err := client.Chat.Completions.New(ctx, openai.ChatCompletionNewParams{
		Model: "anthropic/claude-sonnet-5",
		Messages: []openai.ChatCompletionMessageParamUnion{
			openai.UserMessage("Hello via OpenRouter!"),
		},
	})
	if err != nil {
		log.Fatalf("OpenRouter API call failed: %v", err)
	}

	log.Printf("Response: %s", response.Choices[0].Message.Content)
}

The defer tp.Shutdown(ctx) call is essential. Without it, traces buffered in memory will be lost when your application exits.

Using OpenRouter is a great way to experiment with different models without changing your core instrumentation logic. All calls will be traced by LangWatch, regardless of the underlying model you choose.